Characterization of three putative sub-domains in the signal-input domain of the ArcB hybrid sensor in Escherichia coli(1).

The ArcB sensor plays a crucial role in the histidine to aspartate (His-to-Asp) phosphorelay signal transduction, which is involved in the transcriptional regulatory network that allows Escherichia coli cells to sense various respiratory growth conditions. ArcB is one of the best-studied hybrid His-kinases involved in the multi-step His-to-Asp phosphorelay. However, a major question that remains to be elucidated is: how does ArcB sense an anoxic signal? The N-terminal region of ArcB is considered to be a signal-input domain, which probably plays a role in such signal-perception. In this study, this N-terminal region of ArcB was dissected into three putative sub-domains, a "transmembrane domain," a "leucine-zipper-like domain, " and a "PAS-like domain." The importance of these structural domains was assessed in vivo and in vitro by systematically analyzing a number of arcB mutants, each of which encodes a mutant ArcB protein having an amino acid substitution or a deletion within one of these sub-domains. The results are discussed with special reference to the nature of the ArcB anaerobic sensor.